[Bug tree-optimization/78847] pointer arithmetic from c++ ranged-based for loop not optimized

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78847

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amker at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
And the real inefficiency is niter analysis returning unsimplified

(unsigned long) &MEM[(void *)&foo + 9B] - (unsigned long) ((const char *)
&foo.ascii_ + 1)

from here:

#1  0x000000000134f088 in number_of_iterations_ne (loop=0x7ffff5534550, 
    type=<pointer_type 0x7ffff569f3f0>, iv=0x7fffffffd4b0, 
    final=<addr_expr 0x7ffff51b4620>, niter=0x7fffffffd5e0, 
    exit_must_be_taken=true, bnds=0x7fffffffd3d0)
    at /space/rguenther/src/svn/gcc-7-branch/gcc/tree-ssa-loop-niter.c:991
991                            fold_convert (niter_type, iv->base));
(gdb) l
986       else
987         {
988           s = fold_convert (niter_type, iv->step);
989           c = fold_build2 (MINUS_EXPR, niter_type,
990                            fold_convert (niter_type, final),
991                            fold_convert (niter_type, iv->base));

where

final: &MEM[(void *)&foo + 9B]
iv->base: (const char *) &foo.ascii_ + 1

one could either try to enhance the associate: case of fold_binary or use
tree-affine above, like with

Index: gcc/tree-ssa-loop-niter.c
===================================================================
--- gcc/tree-ssa-loop-niter.c   (revision 245276)
+++ gcc/tree-ssa-loop-niter.c   (working copy)
@@ -42,6 +42,7 @@ along with GCC; see the file COPYING3.
 #include "tree-chrec.h"
 #include "tree-scalar-evolution.h"
 #include "params.h"
+#include "tree-affine.h"


 /* The maximum number of dominator BBs we search for conditions
@@ -986,9 +987,12 @@ number_of_iterations_ne (struct loop *lo
   else
     {
       s = fold_convert (niter_type, iv->step);
-      c = fold_build2 (MINUS_EXPR, niter_type,
-                      fold_convert (niter_type, final),
-                      fold_convert (niter_type, iv->base));
+      aff_tree aff_ivbase, aff_final;
+      tree_to_aff_combination (iv->base, niter_type, &aff_ivbase);
+      tree_to_aff_combination (final, niter_type, &aff_final);
+      aff_combination_scale (&aff_ivbase, -1);
+      aff_combination_add (&aff_ivbase, &aff_final);
+      c = aff_combination_to_tree (&aff_ivbase);
     }

   mpz_init (max);


though this is horribly incomplete (fixes the testcase though) and if, then
niter analysis should use aff_trees throughout (not re-build trees for the
intermediate stuff).  With that patch we immediately get '9' as the
number of iterations and thus ldist produces

  <bb 2> [10.00%]:
  _18 = buf__9(D) + ptr_6(D);
  __builtin_memcpy (_18, &foo, 9);